Center high mount stop lamps are provided on vehicles to enhance vehicle braking indication to following vehicles. Such stop lamps are particularly advantageous in situation where the conventional outboard brake lights are obscured by one or more vehicles interposed between the lead vehicle and a following vehicle. A lead vehicle's center high mount stop lamp is generally visible to a following vehicle operator through the passenger compartments of intermediate vehicles thus providing an indication to the following vehicle operator of preceding traffic conditions several car lengths ahead.
Until recently, standard incandescent bulbs have been the illumination source of choice for center high mount stop lamps. A typical center high mount stop lamp has one or more incandescent bulbs incorporated into a reflective housing adapted to emit light through a light transmissive cover. The light transmissive cover passes selected red wavelengths. Typically, an additional light diffuser is in the transmissive path or light diffusive optics are incorporated as part of the light transmissive cover. Such arrangements provide adequate diffusion of the light emitted such that off axis light output meets certain minimum illumination requirements.
Another type of illumination source becoming more prevalent in center high mount stop lamp applications is the light emitting diode (LED). Advantages of light emitting diodes in such application are low power consumption and long life. LEDs are characterized by a substantially more collimated light output than conventional incandescent bulbs. Additionally, light output equivalent to conventional incandescent bulbs requires a plurality of LEDs. Hence, to meet on and off axis illumination requirements, a large number of individual LEDs is generally required. Certain LED center high mount stop lamps employ a very large number of LEDs spanning a substantial portion of the cross car width which enhances the off axis illumination. Other LED center high mount stop lamps employ fewer LEDs by incorporating lens optics to control the spread of light to meet the illumination requirements. The latter LED center high mount stop lamp requires relatively tight tolerancing of the relationship between the LEDs and lensing optics which may be difficult to control in mass production. The former LED center high mount stop lamp is generally more forgiving of assembly variations due to the wider distribution and overall greater light output of the larger number of LEDs.